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The efficacy of dietary β‐glucan supplementation in golden trevally (Gnathanodon speciosus) was evaluated. The fish were fed five different diets supplemented with 0%, 0.05%, 0.10%, 0.20%, and 0.40% β‐glucan for 56 days. After 56 days of culture, survival was the highest when the fish were fed a 0.10% β‐glucan diet. Growth rates were higher in fish fed diets supplemented with all β‐glucan levels. Lymphocytes increased when the fish were fed a diet supplemented with 0.05% β‐glucan, and thrombocytes increased when the fish were fed 0.2% and 0.4% β‐glucan‐supplemented diets. The total aerobic bacteria count in the gut of golden trevally was higher (p < 0.05) and the total Vibrio counts in the gut of golden trevally were lower (p < 0.05) when the fish were fed any level of β‐glucan. Flesh protein content was higher and flesh lipid content was lower when fish were fed β‐glucan‐supplemented diets at levels greater than 0.1%. When challenged with Streptococcus iniae, fish fed diets containing 0.10% or 0.20% β‐glucan exhibited the highest survival rates. The current results suggest that supplementation with 0.05 to 0.2% β‐glucan in the diet would be beneficial for the culture of the golden trevally. [ABSTRACT FROM AUTHOR]

The use of antibiotics in aquatic feed reduces the incidence of disease and enhances growth performance, although it presents harmful effects, such as development of resistant bacteria and accumulation in the natural environment. A variety of immune stimulants including probiotics, prebiotics, synbiotics, phytobiotics, organic acids, nucleotides, antioxidants, microalgae, yeast and enzymes have been used in the aquaculture industry. In recent decades, much attention has been paid to finding a variety of immunostimulants with lower cost which also affect specific and non-specific immunity and improve fish resistance against a wide range of pathogens. These stimulants strengthen the fish's immune system by increasing the number of phagocytes, lysozyme activity and level of immunoglobulin. The use of immune stimulants as an effective tool to overcome diseases and strengthen the immune system of farmed species, leads to the promotion of cellular and humoral defense mechanisms and increases resistance to infectious diseases. Among these immunostimulants used in aquaculture, β-glucans are of particular importance. Glucans are complex polysaccharide compounds extracted from the cell wall of yeasts and fungi. These compounds can stimulate fish growth, survival, and immune function. Therefore, this review discusses the role and importance of β-glucan as a food additive in aquaculture and examines the impact of these compounds on the growth performance, immunity and biochemical parameters of farmed species. [ABSTRACT FROM AUTHOR]

The present study examines host pathogen response in developmental stage of Pterophyllum scalare (angelfish) infected with Aeromonas hydrophila. The study conducted had two different experiments in which the fish were subjected to formalin‐killed Aeromonas hydrophila (FKA) and immunostimulant (β‐glucan) by immersion method. The first experiment had three treatment groups viz., immunized, non‐immunized and control groups and the exposure time ranged between 12 and 32 dph (days posthatch) of larval rearing. The immunized group exhibited a higher fold expression of RAG‐1, RAG‐2 and IgM genes compared with non‐immunized group. The results demonstrated that the vaccination of 12 dph developmental stage prior to bacterial challenge of angelfish makes it more immunocompetent against the pathogens. Moreover, another experiment using β‐glucan was conducted to further examine the development of immune responses in angelfish larvae. The study consisted four treatments containing graded levels of β‐glucan dosages such as 100, 200 and 300 mg/L including a control (0 mg/L) for 20 days from 12 to 32 dph. The higher fold change in mRNA expression of RAG‐1, RAG‐2 and IgM genes was observed in β‐glucan (200 mg/L) treated group as compared to non‐treated and control group. The highest survivability was observed in the immunized group and immunostimulant treated group in the survival analysis. Hence, the present study suggested that either immunization with FKA or β‐glucan (200 mg/L) could be used as a strategy to mitigate the mortality rate and combat infection during the early larval rearing of P. scalare. [ABSTRACT FROM AUTHOR]

Prebiotics, that is, β‐1,3‐glucans are widely used immunostimulants in aquaculture. A 70‐day feeding trial was conducted to investigate the effects of dietary β‐1,3‐glucan on growth performance, feed utilization, antioxidative and immune status of Pacific white shrimp (Litopenaeus vannamei). Six iso‐energetic and iso‐nitrogenous diets with dietary β‐1,3‐glucan levels at 0, 0.04, 0.08. 0.16, 0.32 and 0.64 g kg−1 were fed to six replicates of shrimp (initial mean weight 0.98 ± 0.02 g). The diet with 0.16 g kg−1 β‐1,3‐glucan significantly improved weight gain and decreased feed conversion ratio of the shrimp. Compared with shrimp fed the basal diet, protein efficiency ratio was significantly higher in the β‐1,3‐glucan supplemented groups. Hepatopancreatic amylase activity was significantly increased by the β‐1,3‐glucan supplementation. The 0.16 g kg−1 β‐1,3‐glucan supplemented diet significantly improved serum total superoxide dismutase activity. The lowest hepatopancreatic malondialdehyde content was observed in the 0.64 g kg−1 β‐1,3‐glucan group. This study suggested that appropriate inclusion level of β‐1,3‐glucan can improve the growth performance, feed utilization and improve the antioxidative capacity of Pacific white shrimp, with optimum supplemental level being about 0.156 g kg−1 based on the weight gain in our results. [ABSTRACT FROM AUTHOR]

Beta‐glucans (BGs) can activate the animal's innate immune system, enhancing the primary defence lines against pathogenic insults. The objective of this study was to assess the immune responses of hybrid striped bass (HSB) when exposed to paramylon, derived from Euglena gracilis, or zymosan, derived from Saccharomyces cerevisiae. Two separate trials were conducted to evaluate the efficacy of these immunostimulants as a feed additive or injected intraperitoneally. Five diets were formulated to contain either paramylon or zymosan at two different levels (50 or 100 mg/kg), and no supplementation serving as the control. Blood and head kidney were sampled, and an elevated production of anion superoxide from isolated phagocytes was observed for all supplemented groups when compared to the control. Dietary paramylon at 50 mg/kg increased immunoglobulin levels in the plasma. The second trial was conducted by injecting a BG solution (10 mg of β‐glucan kg‐1 of body weight) and phosphate buffer solution serving as the control. Seven days after injection, blood samples were collected and immunological profiles from whole blood and plasma were significantly (p <.05) affected by the treatments. The results from this study indicate that both dietary and injected paramylon and zymosan modulated the immunological responses of HSB. [ABSTRACT FROM AUTHOR]